1. Field of the Invention:
This invention relates generally to an arc welding machine, and more particularly, to a welding machine having a strap sliding to advance with advance of the welding position wherein an electric conductor is disposed adjacent the strap at a position not facing a welding groove with the electric conductor being insulated from the strap, and electric current being applied to the electric conductor while it is being cooled by water, to thereby control the arc direction.
2. Description of the Prior Art:
This invention relates to an arc welding machine which has prominent effects especially when used for a type of welding commonly referred to as inclined position welding.
Inclined joints are applied to various structures, as for example in upward welding of outer side platings of a tanker. The total weld length of inclined upward joints is almost equal to the total weld length of vertical joints. Although the amount of welding for inclined joints is essentially equal to the amount of welding for vertical joints, no satisfactory welding method capable of providing good inclined joints has been developed in the art.
Welding of the inclined joints has heretofore been accomplished mainly by the electro-gas arc welding method. According to such electro-gas arc welding method, the groove face of a base metal to be welded is surrounded by a pair of front and back straps of copper cooled by water, a wire is continuously fed to a molten pool while a shield gas is being fed from above the molten pool to generate arcs between the top end of the wire and the molten pool, and the wire and base metal are melted by the heat of the arcs to thereby effect welding. Because of such process characteristics of this welding method, the applicable inclination angle is at most 15.degree., and at a larger inclination angle welding cannot be performed substantially automatically. Further, even at a smaller inclination angle, problems and disadvantages such as mentioned below are brought about and no joint portions of good weld conditions can be obtained according to this method.
Inclined joints are roughly divided into three types. In one type, the groove per se is in a vertical plane but the base metal is inclined, as shown in FIG. 1, and is so-called an overhead-inclined joint. In another type, the base metal per se is in a vertical plane but the groove is inclined, as shown in FIG. 3. In still another type, both the base metal and the groove are inclined.
In the welding of a so-called overhead inclined joint, as shown in FIG. 1, the surface area of a molten pool formed between straps 10 and 11 is larger when compared to the plate thickness. Accordingly, it is difficult to spread arcs over the entire surface. Furthermore, the incidence angle of a wire 13 to the molten pool is not rectangular but it is directed toward the back strap 11. As a result, the heat of the arcs is transferred mainly to the back side, and excessive penetration is caused on the back side to generate undercuts 14 on the back side as shown in FIG. 2, while overlaps 15 are formed or incomplete penetration is caused on the front side. More specifically, high temperature molten metal and slag flow toward the back side by the arcs directed toward the back side, and they wash the base metal on the back to thereby cause excessive penetration on the back side of the base metal, which is another cause of generation of undercuts. On the other hand, the high temperature molten metal or molten slag is not distributed to the front side, and therefore, incomplete penetration or overlap is caused. Furthermore, since the amount of slag is insufficient on the front side, the molten metal sometimes has a direct contact with the copper strap and the bead surface is roughened on the front side.
In the case of a so-called down hand inclined joint, the welding is conducted in a state contrary to the welding state in the case of the above-mentioned overhead joint, and defects are similarly caused.
In the case of a so-called three o'clock inclined joint, for the same reason as in the so-called down hand inclined joint, excessive penetration is caused on the upper base metal 16 to form undercuts 14 and incomplete penetration or overlap is caused on the lower base metal 17.
In the case of a combined joint including the above-mentioned so-called overhead inclined joint and so-called 3 o'clock inclined joint, the above causes are combined together and defects, as shown in FIG. 5, are brought about. More specifically, overlaps 15 are formed in the lower portion of the front side, and in other penetration portions of the base metal there are formed undercuts 14.
Even with a view to eliminating the above defects, if the wire-feeding position is let to approach the side (for example, the front side in the case of an overhead joint), similar defects are brought about because the direction of arcs is not changed. In the event the wire is fed such that the incidence angle of the wire is rectangular to the molten pool as indicated by imaginary lines in FIGS. 1 and 3, the above defects are reduced to some extent, but in this case applicable welding conditions are limited and further, the following problems are brought about.
In order to generate arcs vertical to the face of the molten pool, the wire should be fed so that it is not in parallel with the weld line but with a certain angle to the weld line (for example, when the inclination angle of the joint is 45.degree., the wire is fed in the state inclined at 45.degree. to the weld line). If such feeding is performed in a narrow groove, an electricity-applying tip strikes on a base metal or copper strap, and therefore, practical application of this method is difficult. Furthermore, since the upper base metal 16 is molten and the melt is allowed to fall into the molten pool, a fresh surface is always exposed, and as this procedure is repeated, penetration is enlarged in the upper base metal 16. In contrast, in the case of the lower base metal 17 being molten, the melt covers the base metal and no fresh surface is exposed. Accordingly, incomplete penetration is caused.
Down hand butt welding is performed by various arc welding methods, but in many cases, the direction of generation of arcs is not in accord with the intended direction and defects such as incomplete penetration are sometimes brought about.
The foregoing defects may be overcome by disposing an electric conductor electrically insulated from a base metal in the vicinity of a weld groove and applying an electric current to the electric conductor during welding to control the inclination of the arc direction. However, since heat is generated while an electric current passes through the electric conductor, it is necessary to enlarge the sectional area of the electric conductor so as to reduce the current density.
In the case where an electric conductor composed of copper is continuously used for a long time, if a high electric current is applied, it is necessary to drastically increase the sectional area of the electric conductor. If the sectional area of the electricity is too large or a plurality of electric conductors are disposed, it becomes impossible to allow the electric conductor to approach the arc-generating position, and hence, it is impossible to effectively control the inclination of the arc direction.